1. Field of the Invention
The present invention relates to the field of fluid dispensers and especially to a leakage resistant fluid dispensing assembly for dispensing fluids from multiple containers, while simultaneously and instantaneously venting the fluid containers. Fluid from multiple containers, which hold the same or different fluids, is ejected or sprayed through a nozzle of the dispensing assembly. The fluids are dispensed by a single pumping and transfer system in a balanced manner from the containers, while the containers are simultaneously vented.
2. Description of the Related Art
It is desirable to simultaneously dispense more than one type of fluid from multiple fluid containers. This is especially true when the fluids to be dispensed contain some active ingredients that are incompatible when these ingredients are mixed together in a single solution, yet it is desired to dispense both fluids with their active ingredients simultaneously. One fluid might be water and the other a concentrate. Or one container might hold a fluid with an active ingredient, which the fluid in the second container would deactivate. Examples of such pairs of fluids could be a cleaning composition and a bleach, or a pair of stain removing compositions, one an aqueous composition and the other a high-solvent level enzyme containing composition. Whatever the pair of fluids, they are intended to be dispensed simultaneously and in a fixed ratio to each other, the ratio being set either by the design of the system itself, as discussed below, or by some sort of flow adjustment means, as is known in the art. This fixed ratio may be 50:50 or 60:40, for example.
Several problems have consistently arisen with dispensing systems of this type. Venting of the containers, without allowing leakage of the fluid contents of a container, has been a consistent and recognized problem. An unaddressed problem with such a dispensing system is achieving and maintaining constant flow rates from the different containers so that the fluids are dispensed in an equal or pre-determinedly different ratio. The result of unequal flow is the exhaustion of one container while another still contains fluid.
As a pump draws fluid from a rigid container, the fluid drawn from that container must be replaced by air (venting) for pumping to continue. By contrast, non-rigid containers simply collapse as fluid is drawn from them. When a single pump draws fluids from two containers simultaneously, and especially when the fluids being pumped from the different containers have different densities or vapor pressures, the degree and speed of venting of the two containers must be almost exactly the same, or a pressure differential is created between the two containers. This is especially true when the differences in densities of the fluids become more distant from each other. This pressure differential causes fluid to be pumped from the two containers at different rates, which tends to exacerbate the pressure differential. It has been found that the "replacement" speed of the venting of the container must be almost instantaneous to avoid the creation of this pressure differential/ratio problem. The result of this problem is that the desired ratio of the two fluids is not dispensed.
An obvious solution to instantaneous venting is simply to have permanently open vent holes into the fluid containers. This, however, is not a functionally acceptable solution for this type of a dispensing system. Such vent holes would also be leak holes. Fluid leakage through open vent holes would occur when such containers are inadvertently inverted or knocked on their sides. Leakage would also occur if such containers were transported in a low-pressure environment (e.g., the cargo section of an airplane). Additionally, permanently open vent holes would allow vaporization of volatile compounds from within a fluid container. Thus, some means of closing the vent holes is necessary, but the closure mechanism must not in any way impede the flow of air into the container when fluids are being dispensed. Also, the closure mechanism should be relatively simple in construction and inexpensive to manufacture.
While consistency of dispensing is controlled by the venting mechanism of the dispensing apparatus, the ratio of the liquids to be mixed and then dispensed is controlled by the intentional balancing of several interrelated factors: the length and diameters of the dip tubes into the fluid containers, the viscosities and specific gravities of the fluids to be dispensed, the rate of pumping and perhaps, the pumping capacity of the pump. The pumping capacity of the pump is dependent upon the diameter of the internal piston or cylinder and the length of the stroke of the pump.
For consistent dispensing of two distinct fluids, excessive commingling of the fluids before they are dispensed must also be prevented. Commingling of the fluids can happen either because the two fluids are brought together in a larger than necessary fluid transfer channel or because a pressure differential created between the containers causes siphoning between the containers. To prevent this, a balanced valving system must be incorporated into the fluid system of the assembly.
Manually operable pumps for use by individuals are necessarily small and lightweight--and therefore have low displacement capacities and low pressure differentials. Available trigger operated spray pumps have been found to pull pressure differentials below approximately 8 psi (550 millibars).
When fluids are dispensed from multiple fluid containers, a small pressure differential can form without unimpeded and instantaneous venting of the containers. This makes venting a critical factor. With larger capacity, higher pressure differential pumps, flapper valves, ball check valves, duck bill valves or the like covering the vent holes would pop open promptly in response to the action of the pump, which created the pressure differential pull. But small pressure differentials mean that small differences in the behavior of the materials or components of a venting system can produce unbalanced venting. For example, deformable materials for use in components of items for mass consumer use are neither precision formulated nor configured. Thus, one flapper valve of a pair might be more or less rigid than the other, and one could flex open in response to a small pressure differential pull before the other, creating unequal venting with the problems described before.
U.S. Pat. No. 5,152,461 (hereinafter referred to as "the '461 patent") to Proctor, "Hand Operated Sprayer With Multiple Fluid Containers" discloses a trigger sprayer dispensing device that selectively draws fluids out from at least two containers, mixes the fluids in a desired concentration or ratio and expels the mixture of fluids out of a nozzle. This trigger sprayer is equipped with a metering device for variably controlling the ratio of fluids being mixed. The containers connected to the trigger sprayer are selectively detachable for refilling a container with fluid or exchanging one of the containers with another container having another fluid.
The '461 patent utilizes a piston and cylinder fluid pumping mechanism, which is located near the nozzle outlet. When the piston draws a vacuum within the cylinder, fluid is drawn up from the first and second bottles, through connecting tubings to the cylinder and out the nozzle. The first and second connecting tubings are made of flexible material so that as the piston reciprocates, the tubings flex back and forth with the piston movement. The piston is provided with a disk-shaped diaphragm installed on its downstream end, which acts as a flapper or butterfly type one-way valve. When at rest, the valve provides positive sealing pressure to inhibit fluid leaking from the chamber back into the bottles, and to inhibit siphoning of fluids between the bottles through the chambers. In the '461 patent, the bottles are individually vented through vent holes having one-way valving mechanisms. The vent holes are provided in tube retainer pieces. Each bottle has its own tube retainer piece, and hence, its own vent hole. To prevent liquid from undesirably leaking out through the vent holes, the venting mechanisms comprise tubular-shaped retainer seals that act as one-way valves. Each bottle likewise has its own retainer seal.
Accordingly, the '461 patent recognizes the need to vent the bottles, but provides a complicated valving arrangement to do so. The dispensing mechanism, with its own separate butterfly-type valve, adds to the complexity of the device in the '461 patent. Such a complex system can be difficult and expensive to manufacture. These costs will be passed on to the consumer. Further, such a complex valving arrangement can fail for one reason or another, for reasons such as those discussed above.
Further, while the '461 patent recognizes the need for venting the bottles, that patent does not recognize the need for instantaneously venting of the bottles upon dispensing of the liquids. Rather, venting is independent for each bottle and a finite or minimum "cracking" pressure is required to open a respective vent hole. Thus, a predeterminedly minimum negative pressure or partial vacuum must be generated in each bottle to open a respective vent hole. With this arrangement, any small differences in the negative pressure necessary to open a respective vent hole will magnify the pressure differentials in dispensing the fluids. This will exacerbate any problems in maintaining a desired dispensing ratio, and can cause premature siphoning of the fluid in one of the containers.